Daniel is 5 times as old as Luis and is also 8 years older than Luis. How old is Daniel?
Explanation: We can use the given information to write down two equations that describe the ages of Daniel and Luis. Let Daniel's current age be $d$ and Luis's current age be $l$ $d = 5l$ $d = l + 8$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $d$ is to solve the second equation for $l$ and substitute that value into the first equation. Solving our second equation for $l$ , we get: $l = d - 8$ . Substituting this into our first equation, we get the equation: $d = 5$ $(d - 8)$ which combines the information about $d$ from both of our original equations. Simplifying the right side of this equation, we get: $d = 5d - 40$ Solving for $d$ , we get: $4 d = 40$ $d = 10$.